422 Unprocessable Entity was never part of the official spec, but it was used because the official definition of 400 Bad Request in RFC 2616 was too strict and only covered cases when the client sent a request with malformed syntax.
RFC 7231 expands the definition of 400 Bad Request to include anything perceived to be a client error, removing the need for a separate 422 response.
AS much as possible we adher to [RFC 7540] (https://tools.ietf.org/html/rfc7540#section-8.1.2)
Just as in HTTP/1.x, header field names are strings of ASCII characters that are compared in a case-insensitive fashion. However, header field names MUST be converted to lowercase prior to their encoding in HTTP/2. A request or response containing uppercase header field names MUST be treated as malformed (Section 8.1.2.6).
An origin server MUST NOT send a Date header field if it does not have a clock capable of providing a reasonable approximation of the current instance in Coordinated Universal Time. An origin server MAY send a Date header field if the response is in the 1xx (Informational) or 5xx (Server Error) class of status codes. An origin server MUST send a Date header field in all other cases.
https://tools.ietf.org/html/rfc7231#section-7.1.1.2
Any server may be incapable of providing accurate time and date information.
For this reason Raxx delegates handling the Date header to the server underneath it.